1. Field of the Invention
The present invention relates to radio communication apparatus which include a base unit connected to a communication line and radio terminals connected through a radio circuit and, more particularly, to apparatus which limit the duration of a ring tone generated by a radio terminal to thereby reduce the consumption of a battery of the radio terminal and to greatly prolong the time in which the radio terminal is used in a non-charged state.
2. Description of the Related Art
FIG. 7 is a block diagram of a radio communication apparatus of this type in which a base unit 1 is connected via a radio circuit to a radio telephone set 2 and also to a telephone line 3.
The signal delivered via the telephone line 3 is supplied as a modulation input to a transmitter 5 via a hybrid circuit 4. The signal modulated by and output from the transmitter 5 is transmitted as waves to the radio telephone set 2 via a transmitting antenna 6.
The waves transmitted by the radio telephone set 2 are received by a receiving antenna 7 and demodulated by a receiver 8 of the base unit. The demodulated signal is delivered by the hybrid circuit 4 to the telephone line 3.
A synthesizer 9 delivers to the transmitter 5 and receiver 8 a signal having a frequency corresponding to a radio channel.
One of the outputs from the receiver 8 is input to a received-field intensity detector 10 in order to determine the field intensity. The circuit 10 is generally called a carrier squelch circuit or a noise squelch circuit. Another output from the receiver 8 is delivered as a data signal contained in the demodulated received signal to an identification signal detector 11 which checks an identification signal determined by the combination of the base unit 1 and radio telephone set 2. The identification signal is generally called an ID code signal.
The output from the detector 11 and the modulated data signal are input to a control circuit 12 for use in the connection control. The control circuit 12 controls the synthesizer 9 to provide switching control between radio channels or to cause a transmission data signal to be input as a modulation input to the transmitter 5.
The radio telephone set 2 also includes a receiving antenna 13, a receiver 14 and a transmitting antenna 18. The demodulated output from the receiver 14 is delivered to a telephone receiver 15. The voice input to a telephone transmitter 16 becomes a modulation input to the transmitter 17 and the resulting modulated signal is transmitted via the transmitting antenna 18.
A synthesizer 19, a received-field intensity detector 20, and an identification signal detector 21 are similar to the corresponding ones of the base unit 1. A control circuit 22 provides the entire control of the radio telephone set 2. A speaker 23 is a sounder which generates a ring tone when there is an incoming call. A power source for these elements in the base unit includes an AC plug 24 connected to an AC 100 V source and a rectification stabilizing circuit 25, the outputs of which are provided to the respective required elements. The output from the stabilizing circuit 25 is supplied to a chargeable battery 29 for the radio telephone set 2 via a current restricting resistor 26 via a pair of charging terminals 27 and 28. The output from the battery 29 is used as a power source for the radio telephone set 2. Reference numeral 31 denotes a power source switch for the telephone set 2; 32, a dial key unit used for transmitting a call; and 33, a line relay forming a direct current loop.
The control of this conventional apparatus when there is an incoming call is outlined as follows. When an incoming signal detector 30 of the base unit 1 detects an incoming signal from the telephone line 3 when the base unit is in a standby state, it sets the oscillating frequency of the synthesizer 9 to a control channel frequency, and turns on the transmitter 5 to cause same to transmit the incoming signal which contains a signal designating a talking channel S-CH.
The radio telephone set 2 turns on the synthesizer 19 for a predetermined interval of time t1 in its standby state, sets the oscillating frequency of the synthesizer at the control channel frequency and turns on the receiver 14. When the incoming signal is received, the telephone set 2 turns on the transmitter 17 to cause same to deliver an answer signal and selects the designated talking channel S-CH. Unless an incoming signal is received, the synthesizer 19 and receiver 14 are turned off for a predetermined interval of time t2.
When the base unit 1 detects the waves from the radio telephone set 2 using the received-field intensity detector 10, it stops transmission of the incoming signal. Unless waves from the radio telephone set 2 are detected, the base unit continues to transmit the incoming signal up to a predetermined number of times n. The transmission continues because the radio telephone set 2 is in an intermittent reception state in which the telephone set cannot receive signals for the interval of time t2. The reason why the transmission is stopped after it is performed up to n times is to avoid useless occupation of the control channel when the power source for the telephone set 2 is off or the telephone set 2 is at a great distance from the base unit.
If the ID code signal contained in the answer signal from the telephone set 2 coincides with a preset code, the base unit 1 selects the talking channel S-CH designated by the incoming signal. If not, the base unit 1 waits for the disappearance of the call from the telephone line 3 and then returns to the standby state thereof because there may be a response from a radio telephone set on another set.
After the base unit 1 selects the channel S-CH, it delivers a bell ring signal. When the telephone set 2 receives this signal, it generates a ring tone from a speaker 23. If the telephone set 2 responds to the ring tone by going off-hook, it sends an off-hook signal to the base unit to thereby enable communication.
When the base unit 1 receives the off-hook signal, it stops transmission of the bell ring signal and closes the line relay 33 to establish a talking loop via the telephone line 3 to thereby enable telephone communication.
When the telephone set 2 transmits a call signal, the telephone set 2 and base unit 1 operates as follows. When the telephone set 2 performs a calling operation on the telephone line 3, the control circuit 22 determines that it should shift to the transmitting operation, locks the oscillating frequency of the synthesizer 19 to the control channel frequency, and turns on the receiver 14 to thereby cause same to receive waves at the control channel C-CH. The control circuit 22 detects the field intensity of the received waves at the control channel C-CH using the output detection signal from the received-field intensity detector 20. Unless the received-field intensity is higher than a predetermined value, the control circuit 22 determines that the control channel is idle and turns on the transmitter 17 to thereby cause same to transmit the ID code signal allocated to the telephone set 2. When the base unit 1 receives the ID code signal, it checks whether the ID code signal coincides with the ID code allocated to the combination of the base unit 1 and telephone set 2. If so, the base unit 1 turns on the transmitter 5 to cause same to transmit to the telephone set 2 an answer signal comprising the ID code and data designating S-CH.
When the telephone set 2 receives the answer signal from the base unit 1 through the control channel, it checks whether the ID code signal contained in the answer signal coincides with the ID code allocated to the telephone set 2. If so, the telephone set 2 changes the oscillating frequency of the synthesizer 19 to the frequency of the talking channel designated by the base unit 1.
After the base unit 1 has transmitted the answer signal, it also changes the oscillating frequency of the synthesizer 9 to the frequency of the talking channel designated for telephone communication. Thus the base unit 1 and telephone set 2 are connected through the talk channel designated by the base unit 1. Thereafter, by an dialing operation using dial key unit 32, the telephone set connected through the telephone line 3 is called to enable telephone communication.
As will be understood from the above description, when there is an incoming signal on the telephone line 3, the base unit 1 causes the speaker 23 to generate a ring tone until the telephone set 2 responds by the off-hook operation. Therefore, when there is no user at the telephone set 2 or in a range in which the ring tone reaches the user, the speaker 23 continues to generate the ring tone until the caller at the telephone line 3 terminates the attempted call. As a result, as long as there is an incoming signal on the telephone line 3, the battery 29 is consumed and eventually the telephone set 2 will cease to function.
It is an object of the present invention to provide a radio communication apparatus which reduces the consumption of the battery for a radio telephone set.